The present invention relates to color television picture tube electron guns. The electron gun generates an electron beam which is directed and accelerated by an electrostatic field. The electron beam impinges the luminescent elements which make up the picture tube screen. A conventional picture tube utilizes a horizontally sweeping electron beam raster, and this regular periodic raster beam should go visually undetected in order to minimize viewer distraction with the entire image formed on the screen. The regularity of the raster can give rise to optical interference patterns. It is known that an astigmatic electron lens can be used to alter and shape the electron beam area which impinges the phosphor screen to minimize optical distractions. Such an astigmatic lens is taught in U.S. Pat. No. 3,852,608 in which the electron beam is elongated in the direction normal to the raster sweep direction.
The astigmatic element is described as two plates, which are segments of a circle which are attached to the end closure portion of the second electrode of the electron gun. The plates are disposed on the side of the end closure facing the third electrode. The plates define an elongated passage about a centralized beam admitting aperture in the second electrode end closure. Such plates require a separate fabrication and assembly operation. The reference patent also teaches a unitary second electrode astigmatic lens in another embodiment, in which the end closure of the second electrode is provided with an elongated bulge formed in the end closure of the second electrode. The elongated bulge extends toward the first electrode.